This application claims priority to Japanese Patent Application No. JP2000-245436, filed on Aug. 11, 2000, in Japan. The contents of the aforementioned application are hereby incorporated by reference.
The present invention relates to a fuel cell stack comprising a plurality of fuel cell units horizontally laminated alternately with separators and firmly fastened by a plurality of insulator-coated rods penetrating holes of the fuel cell units.
For instance, a solid polymer electrolyte-type fuel cell battery usually comprises a fuel cell stack constituted by laminating a plurality of fuel cell units with separators, each fuel cell stack comprising an electrolytic membrane composed of an ion exchange polymer membrane (cation exchange membrane) and an anode and a cathode disposed on both sides of the electrolytic membrane, the fuel cell stack being fastened by a plurality of bolts. In this type of a fuel cell battery, a fuel gas (hydrogen-containing gas) supplied to the anode is turned to hydrogen ions on a catalytic electrode, and migrates through the properly wet electrolytic membrane to the cathode, with electrons released by ionization withdrawn to an external circuit for use as DC electric energy. An oxidizing gas (oxygen-containing gas or air) is supplied to the cathode, at which hydrogen ions react with electrons and oxygen to form water.
Such fuel cell stack is properly mounted onto a vehicle, etc. at a position under a floor thereof, and in this case, the fuel cell stack is desirably as small as possible in height dimension. For this purpose, the fuel cell stack should be mounted horizontally onto the vehicle, with each fuel cell unit and each separator being laminated horizontally.
To fasten the laminated fuel cell units and separators, as shown in FIGS. 14 and 15, fixing members 11, 11 such as end plates, etc. are conventionally disposed on both sides of the fuel cell stack, and backup plates 14, 14 disposed outside the fixing members 11, 11 have a plurality of holes 14a, 14a for receiving fastening rods 6 having threaded end portions, to which nuts 6c, 6c are screwed. In this case, to ensure electric insulation, each of the fuel cell units and the separators does not have a hole, through which a rod 6 penetrates. With this structure, each of the fuel cell units and the separators is fastened only by sliding friction resistance. Incidentally, 16 denotes a Belleville spring, and 18 denotes a flat washer.
However, the fixing method of a fuel cell stack as shown in FIGS. 14 and 15 is disadvantageous, in the case of horizontally mounting the fuel cell stack, in that vibration, shock, etc. for a long period of time cause the overall fuel cell stack to bend downward, generating gaps between the fuel cell units and separators in their lower portions, though there is no problem in the case of vertically mounting the fuel cell stack. This reason is considered that because a plurality of horizontally extending rods are always subjected to a large load, rods at lower positions tend to expand or bend.
Japanese Patent Laid-Open No. 2000-123857 discloses a solid polymer electrolyte-type fuel cell battery comprising a fuel cell laminate and fixing plates disposed on both ends of the fuel cell laminate for fastening the fuel cell laminate with a plurality of tie rods, each tie rod having an electric insulating layer, a hole of the laminate for receiving each tie rod having a larger inner diameter than an outer diameter of the tie rod to ensure electric insulation between the laminate and the tie rod. The relations of the tie rods 6 to each separator in this fuel cell are shown in FIGS. 16 and 17.
However, the fixing method disclosed in Japanese Patent Laid-Open No. 2000-123857 is disadvantageous in that because there is a gap between each tie rod and an inner surface of each hole, sliding and opening may take place between the fuel cell units and the separators by vibration, shock, etc. for a long period of time, resulting in their lower portions opening.
Accordingly, an object of the present invention is to provide a fuel cell stack constituted by horizontally laminated fuel cell units and separators, which do not slide or open even under vibration, shock, etc. for a long period of time.
The first fuel cell stack of the present invention comprises a horizontal laminate of a plurality of fuel cell units and separators, each fuel cell unit being constituted by an electrolytic membrane sandwiched by an anode and a cathode, and fixing members disposed horizontally on both sides of the laminate, the laminate and the fixing members having a plurality of holes penetrating therethrough in a lamination direction, each hole receiving a rod for fastening the laminate in a lamination direction, at least one of an inner surface of the hole and an outer surface of the rod being provided with an insulator, and the surface of the rod being at least partially in contact with the inner surface of each hole of the laminate via the insulator.
With this structure, each of fuel cell units and separators are firmly fixed together not only by sliding friction resistance but also by a plurality of rods. Accordingly, even if the fuel cell stack were subjected to vibration, shock, etc. for a long period of time, the fuel cell stack would not be bent downward, to such an extent that there arise open gaps between the fuel cell units and the separators in a lower portion of the laminate.
In the first fuel cell stack, it is preferable that the rod is coated with an insulator, an insulator surface of the insulator-coated rod being substantially in contact with an inner surface of each hole of the laminate. More preferably, the insulator surfaces of all insulator-coated rods are substantially in contact with the inner surfaces of the holes of the laminate. With this structure, the fuel cell units and the separators are more firmly fixed by the insulator-coated rods with sufficient insulation.
The second fuel cell stack of the present invention comprises a horizontal laminate of a plurality of fuel cell units and separators, each fuel cell unit being constituted by an electrolytic membrane sandwiched by an anode and a cathode, and fixing members disposed horizontally on both sides of the laminate, the laminate being fastened in a lamination direction by rods disposed outside the laminate and fixed to the fixing members, at least one of an outer surface of the laminate and an outer surface of the rod being provided with an insulator, and the surface of the rod being at least partially in contact with the outer surface of the laminate via the insulator.
With this structure, there is no need to provide the laminate with holes, resulting in decrease in the overall cost of the fuel cell stack. Also, because the surfaces of the rods are at least partially in contact with the surfaces of the laminate, the laminate can be prevented from being bent.
In the second fuel cell stack, it is preferable that the rod is coated with an insulator, an insulator surface of the insulator-coated rod being substantially in contact with the outer surface of the laminate. It is also preferable that the laminate comprises a plurality of horizontal grooves on the surface, and that the insulator-coated rods are substantially in contact with inner surfaces of the horizontal grooves. With the horizontal grooves, the laminate can be in firm contact with the insulator-coated rods.
The third fuel cell stack of the present invention comprises a horizontal laminate of a plurality of fuel cell units and separators, each fuel cell unit being constituted by an electrolytic membrane sandwiched by an anode and a cathode, and fixing members disposed horizontally on both sides of the laminate, a plurality of holes for passing a reaction gas penetrating through the laminate and the fixing members in a lamination direction, each hole receiving a rod for fastening the laminate in a lamination direction, at least one of an inner surface of the hole and an outer surface of the rod being provided with an insulator, and the surface of the rod being at least partially in contact with the inner surface of each hole of the laminate via the insulator. The rod is preferably coated with an insulator, an insulator surface of the insulator-coated rod being substantially in contact with an inner surface of each penetrating hole.